Though i cud write a big proposal that can attract you. but instead of wasting my time, just wanna tell u..
i hv already been wrking fr this kind of project. so, i undrstnd, what u actually want..
Methodology: I'll prefer PHP based backend. the reason that i am not saying google cloud messaging backend.. coz tht will not be much flexible..
Time: though it will just take 3 DayZ.. but for the better functionality i want more time.
it will b gr8 if u cud talk to me on phone..
mukarram(dot)ali89(at)gmail(dot)com
hope to wrk with u..
Happy Eid... :)